I think what you have there are "ground bees", and if they're anything like the ones here, they have a REALLY BAD attitude about disturbances.
I think if I found one of those thirty feet from my well, I'd have a dump truck deliver about a full yard of sand or topsoil, dropping it directly on top of that nest. I'd inform the truck driver about what's going on so he could unlatch the dropgate far away from the nest, then guide the truck (with windows closed) until it was backed up such that the dropgate was directly above the nest, then dump the load.
My second choice would be gas, and my weapon of choice would be argon (readily available in aerosol-type cans under the brand name "bloxygen").
Third choice would be carbon monoxide from a lawn-mower engine's exhaust.
Fourth choice would be a shop-vac.